Process for forming iodine images



July 8, 1947.

A. BARNES ET AL 2,423,473

PROCESS FOR FORMING IODINE IMAGES Original Fil'ed Jan. 12, 1944 fllaLzcuLmeLy OBZENTED Cnwsr.

[Al/76E ,fiuemrd 5 162147210 .Barnea ,i Helen Patented July 8, 1947 UNITED STATES PATENT OFFICE PROCESS FOR FORMING IODINE IMAGES Arthur Barnes, Waltha-m, and Helen R'Husek,

Allston, Mass, assigncrs to Polaroid Corporation, Cambridge, Mass, a corporation of Delaware Original application January 12, 1944, Serial No.

517,982, now Patent No. 2,409,923, dated October '22, 1946. Dividedand this application July 28, 1944, Serial No. 547,096

8 Claims.

and to methods ofproducing said images in such carriers.

This application is a division of our Patent No. 2,409,923, issued October 22. 1946, for Process of forming iodine images.

It is one object of the present invention to provide a novel method of producing images Whose contrast is a function of the direction of vibration of incident light, which-images are known as vectographs and, more specifically, to provide vectographswhichare reproductions I of .photographic images,

Another object of the invention is to provide a novel method of so transforming an image pro duced by exposing and developing a photosensitive emulsionas to produce a corresponding image in a dichroic material.

It is a further object. of the invention to provide a novel-method of chemically transforming an image in silver to an image in iodine.

Further objects of theinvention are the provision of a method of conventionally exposing and developing a silver halide emulsion and thereafter subjecting said emulsion to a plurality of novel chemical transformations whereby iodine replaces the exposed silver halide particles of the plified in .the following disclosure and the scope of the application of which will be indicated in the claims.

This invention contemplates the production of a predetermined image, or the like, by the transformation of a portion of at least the surface area of a non-polarizing material to a polarizing surface, whereby said image is obtained in polarized light. In accordance with the inventionan emulsion of a photosensitive material, such as a silver halide, is exposedand developed, as well underoriginal. emulsion; the provision of a novel meth- 0d of effecting the desired chemical transformation from silver toiodine whereby the iodine image is substantially as sharplyand, as clearly defined in the carrier asjthe original silver image;

'the provision ofa novelphotosensitive emulsion comprising a silver halide, in a molecularly oriented plastic carrier, which carrier when stained with iodine is adapted to render said stain dichroic; the use of an oriented sheet of polyvinyl alcohol surfaced with a conventional silver halide emulsion, as for example, of gelatin, in carrying out the novel transformation of the invention to obtain a corresponding dichroic image; and the provision of a novel method of obtaining an iodine image in an unoriented material and of transferring said image to a molecularly orientedplastic carrier, as by a surface-to-surface contact, for the purpose of producing a corresponding dichroic image in said carrier.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and relation of one of said steps with respect to each of the others, which are exemhol. formations. of .silver.to iodine are Within thescope stood in the art, to form an image in silver and is thereafter subjectedto anovel chemical trans- -which plastic is of such character that iodine is adapted to produce. therein .a light-polarizing stain. In another form of the invention the oriented plastic sheet, instead of forming part of thephotosensitive emulsion from which the silver image is obtained, may constitute a .base or a support for, a conventional silver halide emulsion,

.asior example of gelatin. In still another form of the invention the silver halide emulsion may comprise a suspension of the photosensitive material ina mixture of gelatin and polyvinyl alco- It .isalsoto be understood that other transof the invention, asfor example, a positive print in silver may have the silver image converted to an iodineimagain accordance with the processes of .theinvention, and the latter may then beimprintedbya suitable transfer process on a sheetof oriented plastic to produce in said sheet a dichroicdmage whichwill correspond to the silverimage.

In the -,pr eferred-. embodiments of the present invention, the molecularly oriented carrier in which the dichroicimage is formed. is a sheet of transparent, high molecular weight .polymer adapted to form a dichroic sorption complex with iodine, said polymer preferably containing hydroxyl groups, and examples. of suitable polymers dichroism and hence are more suitable in the production of dichroic images.

In order to obtain the best results with respect to dichrcism in the images of the present invention, at least the surface molecules of the plastic carrier should first be oriented to substantial parallelism. This may be conveniently accomplished by softening the sheet, as for example by subjecting to heat and then stretching or extending the sheet until suitable orientation of the molecules has been obtained. In the case of polyvinyl alcohol, a sheet formed by casting may be placed in satisfactory condition for the formation of dichroic images therein by subjecting the sheet to mechanical stress, as for example, by stretching in a uniform direction until the molecules therein are sufficiently oriented. A stretch of from two to six times the original length of the sheet produces good results. Alternatively, the surface molecules of the sheet of polyvinyl alcohol may be oriented, as by application of linear frictional force thereto, without orienting the molecules throughout the remainder of the sheet.

Where an image in polarized light is to be formed in a molecularly oriented plastic carrier by a chemical transformation of a silver image in said carried to an iodine image, the plastic carrier is preferably one which maintains its orientation and is stable throughout the steps comprising the novel process of the invention and which is capable of supporting a dispersion of the photosensitive material from which the silver image is formed. Polyvinyl alcohol is a preferred material for the plastic carrier for the further reasons that it is stable in, and is permeable by, the solutions which convert and transform the silver halide to a silver image and the silver image to the ultimate dichroic stain of iodine. Polyvinyl alcohol is also relatively insoluble in said solutions so that a sharp dichroic image is obtained, despite the several transformations which constitute the novel process of the invention.

The plastic carrier in any of the processes comprehended by the present invention may be supported on a sheet Id of a transparent plastic, as for example a cellulosic plastic, such as cellulose acetate and cellulose nitrate, or a vinyl compound, such as the vinyl acetals, vinyl acetate, vinyl chloride, the vinyl acetate-vinyl chloride copolymers, or a condensation type superpolymer, such as a polyamide or nylon-type plastic. Cellulose acetate is a preferred material for the support and to form the most satisfactory material for the dichroic image there is bonded to at least one face of a sheet of said acetate, a sheet of molecularly oriented polyvinyl alcohol having a hydroxyl content, preferably in excess of 50%, said polyvinyl alcoho1 sheet being uniformly oriented throughout its entire thickness.

The following description of the invention is given by Wa of example in connection with a material having an oriented carrier provided with a, silver image on only one surface thereof whereby a single image in polarized light is obtained in the final product. It is to be expressly understood, however, that the process is equally applicable to the formation of dichroic images on a material having both of its faces molecularly oriented and constituting part of, or supporting on, both of its oriented faces, silver suspensions providing desired images. The images may be of the same object and may bear a predetermined relation to one another. For example, one

may be the left eye image and the other the right eye image of a stereoscopic pair and the directions of the molecular orientations of the plastic layers carrying said images may be at substantially right angles to one another so that an observer of the iodine images formed from said silver images, provided with a pair of suitably oriented analyzers, may have onl the left eye image rendered visible to his left eye and only the right eye image to his right eye, whereby the object is seen stereoscopically.

In one embodiment of the invention a silver halide emulsion in polyvinyl alcohol is exposed and developed by conventional photographic methods to produce an image in silver in the polyvinyl alcohol, and the silver image is thereafter transformed to an image formed of an oxidizing agent, the latter being adapted to release iodine from an iodide. The polyvinyl alcohol suspension of the oxidizing agent is then reacted in an iodide and a material adapted to dissolve said agent, thereby releasing iodine from the iodide. As a result of this transformation,

' the iodine is physically located at the same points on the exposed surface as the original exposed silver halide particles and forms the desired dichroic image in the polyvinyl alcohol.

One method of transforming a silver image to an iodine image in accordance with the present invention is to react the silver with a solution of a permanganate, as, for example, potassium or sodium permanganate, to form an image comprising the relatively insoluble manganese dioxide. The manganese dioxide image is then reacted with an iodide in the presence of an acid, as, for example, an acid solution of the iodide to release iodine, which replaces the dioxide and forms the image in iodine. Examples of suitable iodides for this step are sodium iodide, potassium iodide and ammonium iodide, and these may be in solution with any of a large number of acids, of which hydrochloric, sulfuric and maleic acids are preferred examples.

It will now be apparent to those skilled in the art that the above method of transforming a silver image to an iodine image will render unnecessary the stopping and fixing of the silver image produced by developing the exposed silver halide-polyvinyl alcohol emulsion, so that one or both of these operations may be eliminated. It is preferable, however, to perform at least the stopping by conventional methods. The entire operation after the stopping can be carried out in daylight, without affecting the quality of the final product. It is preferable also to wash the print after each operation which follows the removal of the silver salts from the emulsion.

The above process can be readily adapted for transforming the silver image of a conventional photographic paper print to an iodine image, which iodine image can then be transferred to a sheet comprising at least a surface layer of molecularly oriented polyvinyl alcohol. In a preferred adaptation of the transfer process, the iodine is not released until the paper print is brought into intimate contact with the polyvinyl alcohol surface. This modification of the process comprises transforming the silver image in the paper print to a manganese dioxide, as described above, and then immersing the print in a solution of an iodide which does not contain an acid. This brings the iodide into intimate contact with the dioxide image, but because of the absence of the acid does not release iodine. The acid for rendering the dioxide capable of effecting the release of the free iodine from the iodide solution is contained in the oriented polyvinyl alcohol surface with which the print is then brought into surface contact. The iodine is thus simultaneously released and transferred to the polyvinyl alcohol surface. The acid, as for example maleic acid, may be introduced into the polyvinyl alcohol surface in any well known manner, as by casting the polyvinyl alcohol layer or sheet with the acid contained in the casting solution.

The following examples of the novel processes of the present invention are given for purposes of illustration, but it is to be expressly understood that the proportions may be varied within wide ranges and that the ingredients may also be varied as specified hereinabove and as will now be apparent to those skilled in the art.

Example 1 A layer or sheet of molecularly oriented polyvinyl alcohol containing, or supporting, a silver halide emulsion and mounted on a suitable supporting sheet, is exposed, developed, and stopped, in accordance with conventional photographic methods. It is preferably Washed in water and is then immersed in a bath consisting of:

Cc. Potassium permanganate, five per cent solution 6 Water 200 ing:

Cc. Potassium iodide, ten per cent solution 100 Hydrochloric acid, N solution 20 The product of this immersion contains an image in iodine. It is preferable to immerse the print in a final fixing bath, which bath contains boric acid to stabilize the dichroic image. The fixing bath may also contain sodium sulfate to prevent softening of the sheet, potassium iodide to provide a control for the color of the image,

and in some instances a weak solution of sodium thiosulfate.

Example 2 A paper print is immersed for about two minutes in a bleaching solution consisting of Potassium permanganate, five per cent solution 6 Water 200 and is thereafter washed thoroughly. It may be cleared in a 2% hydrochloric acid solution and is then dipped in a neutral 10% potassium iodide solution. Thereafter, a sheet comprising an outer layer of molecularly oriented polyvinyl alcohol, containing approximately 10% by weight of maleic acid, is brought into contact with said print whereby iodine is released and is transferred to said sheet to give the desired dichroic image.

It will be noted that in each example given above, it is contemplated that the iodine image will be formed in a sheet of a high polymer which is, molecularly oriented. It is conceivable that the novel transformation of a silver image to an iodine image may be useful in connection with other processes than the formation of dichroic images, and, accordingly, it is expressly understood that unless the claims so specify, they are not limited to the formation of an iodine image in a carrier which is molecularly oriented. Where an oriented carrier is used, i. e., a dichroic image is desired, it is preferable that all those portions of the carrier penetrated by the iodine be molecularly oriented since application of the dichroic material to unoriented portions will produce a nondichroic light-absorbing stain.

As has been previously stated, the foregoing description is illustrative only of operative embodiments of the present invention. It must be emphasized that each step therein is a variable, and that none of the ingredients, times, or proportions for any step or solution are critical except insofar as they may be made so by the other variables. The specific examples given comprise operative embodiments of the invention with which excellent results have been obtained. However, considerable variation is possible in virtually any degree thereof, and one or more solutions or steps can be compensated for in the other steps. It is, accordingly, obvious that no set rules can be given and it would be difficult, if not impossible, even to set outside limits on the ranges of variation.

It should be pointed out also that although the foregoing description emphasizes the formation of iodine images which are duplicates of photographic silver images, the invention is in no way limited to the exclusive use of photographically obtained silver images.

It is to be understood that the term water-insoluble as utilized in the claims in reference to the carrier for the ferric salts refers to an insolubility such as will prevent water solutions from appreciably dissolving said carrier in the time in which the reactions transforming the silverimage to the iodine image takes place.

It is also to be understood that the term image in iodine as used in the claims refers to an image formed of iodine or its complexes.

Since certain changes may be made in carrying out the above process without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a, limiting sense.

What is claimed is:

1. The method of producing an iodine image, which comprises transforming an image in silver in a permeable, relatively water-insoluble carrier to an image comprising manganese dioxide by reacting said silver image with a permanganate, and reacting said last-named image with an iodide in the presence of an acid whereby iodine is released and replaces the dioxide to form an image in iodine.

2. The method of producing a dichroic image, which comprises forming the image in silver in a relatively water-insoluble carrier comprising at least a layer of a permeable molecularl oriented high polymer having an aflinity for iodin and adapted to form a dichroic sorption complex therewith, said layer supporting said silver image, transforming said silver image to an image comprising manganese dioxide, and reacting said last-named image with an iodide in the presence of an acid whereby iodine is released and replaces the dioxide to form an image in iodine.

relatively 3. Th method of producing a dichroic image, which comprises transforming an image in silver in a carrier having at least the layer which supports said silver formed of a molecularly oriented polyvinyl alcohol to an image comprising manganese dioxide by reacting said silver image with a permanganate, and reacting said last-named image with an iodide in the presence of an-acid whereby iodine is released and replaces the dioxide to form an image in iodine.

4. The method of producing a dichroic image, which comprises forming the image in silver in a permeable, relatively water-insoluble carrier, transforming said silver image to an image comprising manganese dioxide, reacting said lastnamed image with an iodide in the presence of an acid whereby iodine is released and replaces the dioxide to form an image in iodine, and bringing into face-to-face contact with said carrier a transparent, molecularly oriented high polymer adapted to form a dichroic sorption complex with iodine and having a greater aifinity for iodine than said carrier.

5. The method of producin a dichroic image, which comprises forming the image in silver in a permeable, relatively water-insoluble carrier, transforming said silver image to an image comprising manganese dioxide, reacting said lastnamed image with an iodide in the presence of an acid whereby iodine is released and replaces the dioxide to form an image in iodine, and bringing into face-to-face contact with said carrier a molecularly oriented polyvinyl alcohol.

6. The method of producing a dichroic image, which comprises transforming an image in silver in a permeable, relatively water-insoluble carrier to an image comprising manganese dioxide, immersing said carrier in an iodide, and

bringing said carrier into face-to-face contact with a transparent, molecularly oriented high olymer containing an acid and adapted to form a dichroic sorption complex with iodine.

7. The method of producing a dichroic image, which comprises transforming an image in silver in a permeable, relatively water-insoluble carrier to an image comprising manganese dioxide, immersing said carrier in an iodide, and bringing said carrier into face-to-face contact with a mol'ecularly oriented polyvinyl alcohol containing an acid.

8. The method of producing an iodine image which comprises transforming an image in silver in a permeable, relatively water-insoluble carrier to an image comprising relatively waterinsoluble manganese dioxide, and efiecting a simultaneous oxidation-reduction reaction between said managanese dioxide and an iodide in an acid medium whereby the iodide is oxidized to iodine which replaces said manganese dioxide to form an image in iodine in said carrier.

ARTHUR BARNES. HELEN P. HUSEK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name v Date 628,012 Manly July 4, 1899 2,204,604 Land June 18, 1940 2,289,715 Land July 14, 1942 2,315,373 Land Mar. 30, 1943 1,214,940 Miller Feb. 6, 1917 1,389,742 Crabtree Sept. 6, 1921 1,574,356 Beebe Feb. 23, 1926 

